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Abstract:

Provided are a radiation emission target and a radiation generating
apparatus that reduce the variation in the output due to operation and
temperature history by maintaining stable adhesion of the layered
radiation target and achieve stable radiation emission characteristics.
The radiation target includes a supporting substrate, a target layer that
emits a radiation when irradiated with an electron beam, and an
interlayer located between the supporting substrate and the target layer.
The interlayer has a thickness of 1 μm or less and contains titanium
as a main component. At least part of the titanium shows the β-phase
at 400° C. or less.

Claims:

1. A radiation target comprising a supporting substrate, a target layer
that emits radiation when irradiated with an electron beam, and an
interlayer located between the supporting substrate and the target layer,
wherein the interlayer has a thickness of 1 μm or less and contains
titanium as a main component, and wherein at least part of the titanium
shows a β-phase at 400.degree. C. or less.

2. The radiation target according to claim 1, wherein the interlayer
contains a β-phase-stabilizing metal as a trace component, the
β-phase-stabilizing metal, when added to pure titanium, lowering a
phase transformation temperature of titanium at which the titanium
changes from being in a state containing only an α-phase to being
in a state containing the β-phase so as to be less than a phase
transformation temperature of pure titanium.

3. The radiation target according to claim 2, wherein the interlayer is
composed of an alloy of the titanium and the β-phase-stabilizing
metal.

4. The radiation target according to claim 2, wherein the
β-phase-stabilizing metal is at least one metal selected from V, Nb,
and Ta.

5. The radiation target according to claim 2, wherein the interlayer
contains the β-phase-stabilizing metal in an amount of 1.5 times or
more the minimum β-phase-stabilizing metal content with which the
α-phase titanium and the β-phase titanium coexist as an
eutectoid at 400.degree. C.

6. The radiation target according to claim 2, wherein the interlayer
contains 3.3 atm % or more and 50 atm % or less of the
β-phase-stabilizing metal.

7. The radiation target according to claim 1, wherein the interlayer is
composed of a polycrystal having an average grain size of 0.1 μm or
less measured in the in-plane direction of the interlayer.

8. The radiation target according to claim 1, wherein the interlayer has
a thickness of 1 nm or more.

9. The radiation target according to claim 1, wherein the supporting
substrate functions as a radiation-transmissive member that transmits at
least part of the radiation emitted from the target layer.

10. A radiation generating tube comprising an envelope; an electron
emission source that emits an electron beam, the electron emission source
being located inside the envelope; and a radiation target that emits
radiation when irradiated with the electron beam, wherein the radiation
target is the radiation target according to claim 1.

11. A radiation generating apparatus comprising a package, a radiation
generating tube disposed inside the package, and a driving circuit that
drives the radiation generating tube, wherein the radiation generating
tube is the radiation generating tube according to claim 10.

12. A radiography system comprising the radiation generating apparatus
according to claim 11; a radiation detector that detects radiation
emitted from the radiation generating apparatus and passing through an
object; and a controller that performs collaborative control of the
radiation generating apparatus and the radiation detector.

13. A method for producing a radiation target, the method comprising the
steps of: forming a first layer containing titanium and at least one
metal selected from V, Nb, and Ta on a substrate; forming a second layer
containing a target metal on the first layer; and performing a
β-phase stabilization treatment in which the first layer is
maintained at 600.degree. C. or more and 1600.degree. C. or less.

14. The method for producing a radiation target according to claim 13,
wherein the β-phase stabilization treatment includes at least one of
a solution treatment in which the first layer is maintained at
900.degree. C. or more and 1600.degree. C. or less and an age hardening
treatment in which the first layer is maintained at 600.degree. C. or
more and 880.degree. C. or less.

15. The method for producing a radiation target according to claim 14,
wherein the solution treatment or the age hardening treatment is
performed before the step of forming the second layer.

16. The method for producing a radiation target according to claim 14,
wherein the solution treatment or the age hardening treatment is
performed in the step of forming the second layer.

17. The method for producing a radiation target according to claim 14,
wherein the solution treatment or the age hardening treatment is
performed after the step of forming the second layer.

18. The method for producing a radiation target according to claim 13,
wherein, in the step of forming the first layer, the amount of the at
least one metal selected from V, Nb, and Ta added to the substrate is
0.035 or more and 1 or less in terms of atomic ratio relative to the
amount of the titanium added to the substrate.

19. A method for producing a radiation generating tube including an
envelope, an electron emission source that emits an electron beam, the
electron emission source being located inside the envelope, and a
radiation target that emits radiation when irradiated with the electron
beam, wherein the radiation target is produced by the method for
producing a radiation target according to claim 13.

20. A method for producing a radiation generating apparatus including a
package, a radiation generating tube disposed inside the package, and a
driving circuit that drives the radiation generating tube, wherein the
radiation generating tube is produced by the producing method according
to claim 18.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a transmission-type radiation
target that is suitable for diagnostic applications, nondestructive
radiography, and the like in the fields of medical and industrial devices
and a method for producing the transmission-type radiation target.

BACKGROUND ART

[0002] A well-known example of the radiation target is a transmission-type
target. Since transmission-type targets have advantages in that an
electron emission source, the target, and a radiation extraction window
can be aligned in a line, the applications of the transmission-type
targets in miniaturized, high-definition radiation generating apparatuses
are expected.

[0003] PTL 1 discloses an anode including a beryllium substrate on which
tungsten is disposed. PTL 1 also discloses a method for preventing
separation of the tungsten from the beryllium substrate, which is caused
by stress generated by a difference in linear expansion amount between
the tungsten and the beryllium substrate, by disposing an interlayer
composed of copper, chromium, iron, titanium, or the like therebetween.
PTL 2 discloses a method for improving cooling efficiency for radiating
the heat generated in a target layer by disposing an interlayer as a
thermal diffusion layer between a metal base material composed of a
copper alloy or a silver alloy and the target layer composed of a metal
material such as molybdenum, chromium, tungsten, gold, silver, copper, or
iron. The interlayer is composed of a mixture of copper or silver with
diamond powder or titanium.

CITATION LIST

Patent Literature

[0004] PTL 1 Japanese Patent Laid-Open No. 2000-306533

[0005] PTL 2 Japanese Patent Laid-Open No. 2002-93355

[0006] Existing transmission-type targets having an interlayer sometimes
show a gradual decrease in the output radiation intensity in test runs.
Although the mechanism that causes the variation in output has not been
clearly determined, it is presumably related to the change in adhesion of
the interlayer.

[0007] An object of the present invention is to reduce the variation in
the output radiation intensity by maintaining adhesion of a target layer
over a prolonged period, and to obtain the stable output radiation in
terms of intensity.

SUMMARY OF INVENTION

[0008] A radiation target according to the present invention includes a
supporting substrate, a target layer that emits radiation when irradiated
with an electron beam, and an interlayer located between the supporting
substrate and the target layer. The interlayer has a thickness of 1 μm
or less and contains titanium as a main component. At least part of the
titanium shows the β-phase at 400° C. or less.

[0009] A method for producing a radiation target according to the present
invention includes the steps of forming a first layer containing titanium
and at least one metal selected from V, Nb, and Ta on a substrate;
forming a second layer containing a target metal on the first layer; and
performing a β-phase stabilization treatment in which the first
layer is maintained at 600° C. or more and 1600° C. or
less.

[0010] Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0011]FIG. 1 is a cross-sectional view illustrating a radiation target
according to the present invention.

[0012]FIG. 2 is a cross-sectional view illustrating a radiation
generating apparatus according to the present invention.

[0013]FIG. 3A is a cross-sectional view illustrating another radiation
target according to the present invention.

[0014]FIG. 3B is a cross-sectional view illustrating another radiation
target according to the present invention.

[0015]FIG. 3c is a cross-sectional view illustrating another radiation
target according to the present invention.

[0016]FIG. 3D is a cross-sectional view illustrating another radiation
target according to the present invention.

[0017]FIG. 4A is a cross-sectional view illustrating a radiation
generating tube according to the present invention.

[0018]FIG. 4B is a cross-sectional view illustrating a radiation
generating tube according to the present invention.

[0019]FIG. 5 is a block diagram of a measuring system for measuring the
output radiation intensity of a radiation generating tube.

[0021]FIG. 7A is a block diagram illustrating a manufacturing process of
a radiation target according to the present invention.

[0022]FIG. 7B is a block diagram illustrating a manufacturing process of
a radiation target according to the present invention.

[0023]FIG. 7c is a block diagram illustrating a manufacturing process of
a radiation target according to the present invention.

[0024]FIG. 7D is a block diagram illustrating a manufacturing process of
a radiation target according to the present invention.

[0025] FIG. 7E is a block diagram illustrating a manufacturing process of
a radiation target according to the present invention.

[0026]FIG. 8 is a block diagram of a radiography system according to the
present invention.

DESCRIPTION OF EMBODIMENTS

[0027] A radiation generating tube 1 will be now described. FIGS. 4A and
4B are cross-sectional views illustrating the radiation generating tube 1
including a radiation target (hereafter, referred to as simply target) 8
according to the present invention. The radiation generating tube 1
includes at least an envelope 6 having an internal space 12 maintained at
a vacuum, an electron emission source 3 disposed inside the envelope 6,
and the target 8. The target 8 is disposed in the envelope 6 and arranged
to face the electron emission source 3 so as to be irradiated with an
electron beam 5 emitted from the electron emission source 3.

[0028] The degree of vacuum in the internal space 12 can be any degree of
vacuum with which the mean free path can be maintained so that the
electrons can at least fly between the electron emission source 3 and the
target 8. The applicable degree of vacuum is 1E-4 Pa or less. The degree
of vacuum in the internal space 12 can be selected accordingly in
consideration of the type of the electron emission source 3 used. In
cases where a cold cathode electron emission source or the like is used,
the degree of vacuum is more preferably 1E-6 Pa or less. Optionally, in
order to maintain the degree of vacuum in the internal space 12, a getter
may be installed in the internal space 12 or in an additional space
communicating with the internal space 12.

[0029] The electron emission source 3 disposed inside the envelope 6 can
be any electron emission source as long as the amount of electron
emission is controllable from the outside of the envelope 6. The hot
cathode electron emission source or cold cathode electron emission source
can be used accordingly. The electron emission source 3 can be
electrically connected to a driving circuit 14 installed outside the
envelope 6 so that the amount of the electron emission and the On-Off
state of the electron emission can be controlled via a current
introduction terminal 4 that penetrates through the envelope 6. The
electron emission source 3 includes an electron emission portion 2. The
electron emission portion 2 can be disposed in any position as long as
the electrons emitted from the electron emission portion 2 impinge the
below-described target 8. As shown in FIGS. 4A and 4B, the electron
emission portion 2 can be arranged to face the target 8. The electron
emission portion 2 is maintained at a negative potential of -10 to -200
kV with respect to the target 8. This causes an electron beam 5 emitted
from the electron emission portion 2 to accelerate to the predetermined
kinetic energy and to impinge the target 8. Optionally, a correction
electrode connected to a correction circuit (not shown) may be disposed
in order to correct the position irradiated with the electron beam or
astigmatic aberration on the target 8.

[0030] A radiation generating apparatus 13 will be now described. FIG. 2
is a cross-sectional view illustrating the radiation generating apparatus
13 that houses the radiation generating tube 1. The radiation generating
apparatus 13 includes a package 11, the radiation generating tube 1
disposed inside the package 11, and a driving circuit 14 that drives the
radiation generating tube 1. Optionally, the package 11 may include a
radiation extraction window 10 composed of glass, beryllium, or the like
that passes the radiation emitted from the target 8. When the radiation
extraction window 10 is disposed, the radiation emitted from the
radiation generating tube 1 is emitted outside through the radiation
extraction window 10. In order to promote heat dissipation from the
radiation generating tube 1, the radiation generating apparatus 13 may be
provided by filling the internal space 17 of the package 11 with an
insulating liquid 18 such as a silicone oil.

[0031] The target 8 will be now described. As shown in FIG. 1, the target
8 has a layered structure that includes at least three layers, namely, a
target layer 82 that contains a target substance, an interlayer 81, and a
supporting substrate 80 that are stacked on top of one another in this
order.

[0032] The target layer 82 is located on one surface of the target 8,
which is on the side irradiated with the electrons. The target layer 82
contains a heavy metal as the target substance. Metals having an atomic
number of 39 or more, such as tungsten and gold, can be used as the
target substance. The thickness of the target layer 82 is determined in
consideration of the targeted radiation energy, the density of the target
layer 82, and the accelerating voltage of incident electrons. The
thickness of the target layer 82 can be 1 to 20 μm, for example.

[0033] The supporting substrate 80 structurally supports the target layer
82 that is a thin film. In order to maintain the strength of the layered
body, the supporting substrate preferably has a thickness (thickness of
substrate) of 100 μm or more. More preferably, the supporting
substrate 80 has a thickness of 500 μm or more, because heat locally
generated in the target layer 82 can be released outside the target 8
efficiently. When the supporting substrate 80 contains a light element
such as beryllium, graphite, or diamond as a main component, a
transmission-type target 8 including the supporting substrate 80
functioning as a radiation-transmissive member can be formed. The
transmission-type target 8 allows forward radiation, which is emitted
from the surface of the target 8 that is on the opposite side (hereafter,
referred to as forward) to the side irradiated with the electron beam 5
(hereafter, referred to as backward), to exit from the radiation
generating tube 1 or the radiation generating apparatus 13. When the
target 8 is made transmissive, the maximum thickness of the supporting
substrate 80 is determined in consideration of the radiation
transmittance of the supporting substrate. For example, when the
transmission-type target 8 includes a supporting substrate 80 composed of
diamond, the supporting substrate preferably has a thickness of 2 mm or
less from the viewpoint of radiation transmittance. Since diamond has a
high melting point, low density, and high thermal conductivity, diamond
is a particularly preferable material that can be used for the supporting
substrate 80 of the transmission-type target 8. The diamond used for the
supporting substrate 80 may have any crystal structure, such as a
polycrystal or a single crystal structure and is preferably a
single-crystal diamond from the viewpoint of thermal conductivity.

[0034] The interlayer 81 will be now described. As shown in FIG. 1, the
interlayer 81 is disposed as an adhesive layer that improves adhesion
between the target layer 82 and the supporting substrate 80. The
interlayer 81 has two connection interfaces respectively connected to the
target layer 82 and the supporting substrate 80.

[0035] When the interlayer 81 has an excessively small thickness, the
anchoring force between the supporting substrate 80 and the target layer
82 become insufficient and cannot maintain adhesion therebetween.
Accordingly, the interlayer 81 preferably has a thickness of at least 1
nm or more, or about 10 layers of atoms or more. In contrast, when the
interlayer 81 has an excessively large thickness, the temperature change
during the radiation output of the target 8 causes the stresses at each
of the interfaces of the layers constituting the target 8 due to the
difference in linear expansivity between the supporting substrate 80 and
the target layer 82. This may result in poor adhesion in microscopic
scale. Accordingly, the interlayer 81 preferably has a thickness of 1
μm or less. The interlayer 81 also serves as a heat transfer layer
that transfers the heat generated in the target layer during the
radiation output of the target 8 to the supporting substrate 80
efficiently. Consequently, an excessively large thickness of the
interlayer 81 results in poor thermal conductivity, which causes the
target 8 to be superheated during the radiation output. This may cause a
variation in the output radiation intensity. Accordingly, the interlayer
81 more preferably has a thickness of 0.1 μm or less. Note that
"during the radiation output" refers to the state in which the target
layer 82 is irradiated with the electron beam 5 emitted from the electron
emission source 3 and emitting radiation with the predetermined
intensity.

[0036] The material for the interlayer 81 needs to be a material with
which a sufficient adhesion can be achieved at the connection interfaces
with the target layer 82 and with the supporting substrate 80. In
addition, in order to maintain a layered structure with the target layer
82 that is to be heated up to about 1000° C., the material for the
interlayer 81 is required to have heat resistance so as not to melt
during the operation of the target 8. The interlayer 81 is characterized
in that the interlayer 81 contains titanium as a main component and at
least part of the titanium shows the β-phase as a low-temperature
phase of 400° C. or less. The interlayer 81 having such
characteristics satisfies the above requirements of heat resistance and
can maintain adhesion of the target 8 and good heat dissipation even when
the target 8 is subjected to cyclic temperature history between
in-operation and at-rest. As a result, the target 8 shows an effect of
maintaining a high output stability over a prolonged period.

[0037] Pure titanium exists in two phases having a transformation
temperature of 882° C. in a temperature region of its melting
point of 1670° C. or less. One is a low-temperature phase referred
to as the α-phase, which is shown in a lower temperature region of
882° C. or less and has a hexagonal close-packed crystal
structure. The other is a high-temperature phase referred to as the
β-phase, which is shown in a higher temperature region of
882° C. or more and having a body-centered cubic crystal
structure. In the present invention, pure titanium refers to titanium
with a purity of 100%, which contains no metal element that forms an
alloy with titanium in the composition. In accordance with the
temperature history in which the target layer 82 is heated up to about
1000° C. during operation, the titanium contained in the
interlayer repeatedly undergoes a phase transition from the α-phase
to the β-phase in the heating-up process and a phase transition from
the β-phase to the α-phase in the cooling-down process.

[0038] The inventors of the present invention have determined the
characteristics of the interlayer that had experienced a plurality of
operational histories, and acquired the knowledge that a target that has
experienced a plurality of operational histories shows a gradual decrease
in radiation output, that the interlayer is a polycrystal including a
plurality of grains, and that an interlayer of the target that has
experienced a plurality of operation histories has a coarse grain size,
which is related to the phase transition from the β-phase to the
a-phase that occurs in the cooling-down process.

[0039] On the basis of this knowledge, the inventors of the present
invention have found that the grains of the interlayer 81 containing
titanium as a main component can be prevented from being coarse by
configuring the interlayer 81 to show the β-phase as a
low-temperature phase, and thereby adhesion of the target 8 can be
maintained even when the target has experienced a plurality of
operational histories.

[0040] The interlayer 81 showing the β-phase as a low-temperature
phase includes an interlayer in which not necessarily all of the titanium
shows the β-phase, but part of the titanium shows the β-phase.
The form in which part of the titanium shows the β-phase includes
the form in which the α-phase and β-phase coexist as an
eutectoid. Note that, in the present invention, the low-temperature phase
refers to a phase in a temperature range of 400° C. or less, but
not a specific phase (α-phase or β-phase) of titanium. The
temperature of 400° C. is a reference temperature associated with
the boundary temperature between in-operation and at-rest temperatures of
the target 8.

[0041] In order to show the β-phase as a low-temperature phase, the
interlayer 81 containing titanium may have a composition containing a
β-phase-stabilizing metal as a trace component as well as titanium
as a main component. In addition, the interlayer 81 may be composed of an
alloy of titanium and a β-phase-stabilizing metal. The
β-phase-stabilizing metal is a metal that, when being added to pure
titanium, has an effect of lowering the phase transformation temperature
of titanium at which the titanium changes from being in a state
containing only the a-phase to being in a state containing the
β-phase so as to be less than the phase transformation temperature
of pure titanium. Referring to FIG. 6, the β-phase-stabilizing metal
will be now described in detail with vanadium as an example. FIG. 6 is an
equilibrium diagram of the titanium-vanadium system. The liquidus starts
at a point at 1670° C. at which the vanadium content is 0 atm %
(pure titanium), passes through a point at 1608° C. at which the
vanadium content is 31 atm %, and connects to a point at 1914° C.
at which the vanadium content is 100 atm % (pure vanadium). When
operating in the temperature range below the liquidus, the target 8
maintains adhesion between the layers because the interlayer 81 thereof
is not molten. In pure titanium (vanadium content: 0 atm %) shown in FIG.
6, two branch curves extend from the α-β phase transition
point of 882° C. in the direction of higher vanadium content.
According to one of the branch curves (referred to as first
transformation curve) lying on the lower temperature side, titanium shows
only the α-phase when the vanadium content is less than that of any
composition lying on the first transformation curve. In contrast, when
the vanadium content is more than that of any composition lying on the
first transformation curve, the titanium shows a phase in which both the
α-phase and β-phase coexist as an eutectoid in a ratio based
on the vanadium content. According to the other branch curve (referred to
as second transformation curve) lying on the higher temperature side,
titanium shows a phase in which both the α-phase and β-phase
coexist as an eutectoid in a ratio based on the vanadium content when the
vanadium content is less than that of any composition lying on the second
transformation curve. In contrast, when the vanadium content is more than
that of any composition lying on the second transformation curve,
titanium shows only the β-phase.

[0042] As shown above, the addition of vanadium to pure titanium modifies
the phase-transition temperature characteristics in terms of lowering the
α-β phase-transition temperature (phase transition point) so
as to be less than that of pure titanium, that is, 882° C.
Therefore, vanadium is a β-phase-stabilizing metal for titanium.

[0043]FIG. 6 illustrates only the temperature region of 400° C. or
more. In the low-temperature region of less than 400° C., no
significant change is observed compared with the temperature dependency
of the first transformation curve in the temperature region of more than
400° C. In addition, in order to determine the composition of the
interlayer 81, the behavior of the first transformation curve at
400° C. or more can be sufficiently applied. Thus, the temperature
region less than 400° C. in the equilibrium diagram is omitted.

[0044] The maximum content of β-phase-stabilizing metal in the
interlayer 81 is preferably 50 atm % or less, which means that the
interlayer 81 contains titanium as a main component and
β-phase-stabilizing metal as a trace component. The interlayer 81
needs to contain titanium as a main component and
β-phase-stabilizing metal as a trace component so that the
interlayer 81 achieves static adhesion to the target layer 82 and to the
supporting substrate 80. Static adhesion refers to adhesion between
layers that has no relation to the temperature history but that is mainly
governed by the compatibility between the materials respectively
contained in each layer.

[0045] The minimum content of β-phase-stabilizing metal in the
interlayer 81 can be determined from the first transformation curve.
Specifically, in order to obtain dynamic adhesion, the interlayer 81
preferably contains β-phase-stabilizing metal in an amount of 1.5
times or more the minimum β-phase-stabilizing metal content with
which the α-phase titanium and the β-phase titanium coexist as
an eutectoid at 400° C. Dynamic adhesion refers to adhesion
between layers that changes with the temperature history upon the
occurrence of a phase transition.

[0046] The β-phase-stabilizing metal for titanium is not limited to
the above vanadium (V) and other examples thereof include niobium (Nb)
and tantalum (Ta). In other words, the β-phase-stabilizing metal
contained in the interlayer 81 of the target 8 is at least one metal
selected from V, Nb, and Ta. The interlayer 81 may contain other elements
as long as the effect of lowering the β-α phase transition
temperature of pure titanium is not impaired.

[0047] The minimum vanadium, niobium, and tantalum contents with which the
a-phase titanium and the β-phase titanium coexist as an eutectoid at
400° C. are 2.2 atm %, 1.8 atm %, and 2.0 atm %, respectively,
which are almost the same content. Thus, by containing 3.3 atm % or more
and 50 atm % or less of the β-phase-stabilizing metal, the
interlayer 81 can show the β-phase as a low-temperature phase stably
regardless of the type of the β-phase-stabilizing metal.

[0048] When the interlayer 81 is composed of a polycrystal with an average
grain size of 0.1 μm or less in the in-plane direction of the
interlayer 81, coarsening of the grains of titanium may be prevented to a
higher degree even in the cases where the interlayer 81 has a long
operational and temperature history.

[0049] The method for producing the target 8 will be now described with
reference to FIGS. 7A to 7E. As shown in FIG. 7A, a substrate (supporting
substrate) 80 is prepared. Then, as shown in FIG. 7B, a first layer
(interlayer) 81 is formed on the substrate 80. As a method for forming
the first layer, dry-deposition techniques such as sputtering, vacuum
deposition, and CVD and a method that includes performing a
wet-deposition technique such as spin-coating or ink-jet printing and
subsequently baking the resultant layer can be applied. In the step of
preparing the substrate 80, at least the surface on which the first layer
81 is to be formed is preferably cleaned to remove organic matter prior
to deposition. Then, as shown in FIG. 7c, a second layer (target layer)
82 is formed on the first layer. As a method for forming the second
layer, a sputtering method, vacuum deposition, CVD method, or the like
can be applied accordingly.

[0050] The amount of each metal component added to the substrate 80 in the
step of forming the first layer in the method for producing the target
according to the present invention will be now described. The preferred
β-phase-stabilizing metal concentration
C.sub.β=[M.sub.β/([M.sub.β]+[MTi]) in the interlayer
81 is represented by the following general formula (1):

0.033≦[M.sub.β]/([M.sub.β]+[MTi])≦0.5
general formula (1)

[0051] where [M.sub.β] is the β-phase-stabilizing metal
concentration in the interlayer 81 mentioned above, and [MTi] is the
titanium concentration in the interlayer 81.

[0052] By transforming the general formula (1) into a formula for the
content ratio [M.sub.β]/[MTi], the general formula (2) can be
uniquely obtained.

0.035≦[M.sub.β]/[MTi]≦1 general formula (2)

[0053] Thus, the method for producing the target according to the present
invention includes setting the amount (corresponding to [M.sub.β])
of at least any metal selected from vanadium, niobium, and tantalum added
to the substrate 80 to be 0.035 or more and 1 or less in terms of atomic
ratio relative to the amount (corresponding to [MTi]) of titanium
added to the substrate 80 in the step of forming the first layer.

[0054] The method for producing the target according to the present
invention includes performing the below-described β-phase
stabilization treatment at least on the first layer 81. The β-phase
stabilization treatment step includes heating the first layer 81 and
thereby gives the first layer an effect of stably maintaining a
composition containing titanium that shows the β-phase as a
low-temperature phase. The β-phase stabilization treatment step
includes maintaining the first layer 81 in the temperature range of
600° C. or more and 1600° C. or less for a predetermined
time. More specifically, the heating treatment includes at least one of
the following treatments: a solution treatment in which the first layer
81 is maintained in the temperature range of 900° C. or more and
1600° C. or less for a predetermined time and then rapidly cooled
and an age hardening treatment in which the first layer 81 is maintained
in the temperature range of 600° C. or more and 880° C. or
less for a predetermined time. Selection of the solution treatment and
the age hardening treatment can be made accordingly in consideration of
heat resistance or the like of the target 8 or other members of the
radiation generating tube 1.

[0055] The β-phase stabilization treatment step may be performed in
the step of forming the first layer 81, that is, before the step of
forming the second layer in the production process for the target 8. This
is because diffusion at the interface between the supporting substrate 80
and the interlayer 81 is thereby promoted, which selectively improves
adhesion between the supporting substrate 80 and the interlayer 81.

[0056] The β-phase stabilization treatment step may be performed in
the step of forming the second layer 82 in the production process for the
target 8. This is because the migration of the target material on the
first layer in the deposition process of the second layer is thereby
promoted, which improves adhesion between the interlayer 81 and the
target layer 82.

[0057] The β-phase stabilization treatment step may be performed
after the step of forming the second layer 82 in the production process
for the target 8. This is because the residual stress generated between
layers due to the difference in linear expansivity between the stacked
layers of the target 8 is thereby reduced, which reduces the distortion
and separation of the layered target.

[0058] The heating time for the solution treatment may be determined in
consideration of the type of material or the thicknesses of the
substrate, first layer, and second layer. For example, the heating time
for the solution treatment can be in the range of 10 minutes to 10 hours.
The heating time for the age hardening treatment can be in the range of
20 minutes to 20 hours.

[0059] The manner in which the interlayer 81 and the target layer 82 are
stacked on the supporting substrate 80 is not limited to that in which
the entirety of one surface of the supporting substrate 80 is covered as
shown in FIG. 1 but may be any of the covering techniques shown in FIGS.
3B to 3D. With regards to the covering areas of the interlayer 81 and the
target layer 82, it is preferable in order to prevent the supporting
substrate from becoming charged, to cover the supporting substrate 80
with the interlayer 81 so that the covered area contains at least the
area on the target 8 irradiated with a bundle of the electron beam 35 as
shown in FIG. 3A. It is preferable in terms of adhesion to form the
covering area of the target layer 82 so as to be the same as or included
in the covering area of the interlayer 81. Optionally, according to the
present invention, in consideration of the electrical connection to the
shield 7 or an anode member 21, a portion with which the shield 7 and the
target layer are electrically connected to each other through a
conductive connecting member (not shown), may be formed in the covering
(deposition) area of the interlayer 81.

[0060] Examples of available methods for fixing the target 8 to the shield
7 include a method using a conductive connection member such as silver
solder (not shown) and a method of pressure-bonding.

[0061] The radiation generating apparatus 13 and the radiation generating
tube 1 may include not only one each of electron emission source 3 and
target 8 as shown in FIG. 2 but a plurality of each of electron emission
source 3 and target 8. In the latter case, a plurality of radiation beams
may be emitted independently of or in collaboration with each other.

[0062]FIG. 8 is a block diagram illustrating a radiography system
according to the present invention. A system controller 102 performs
collaborative control of a radiation generating apparatus 13 and a
radiation detector 101. Under the control by the system controller 102, a
control unit 105 outputs various control signals to a radiation tube 1.
The control signals control the state of radiation emitted from the
radiation generating apparatus 13. The radiation emitted from the
radiation generating apparatus 13 passes through an object 104 and is
detected with a detector 108. The detector 108 converts the detected
radiation into a picture signal and outputs the picture signal to a
signal processing unit 107. Under the control by the system controller
102, the signal processing unit 107 performs predetermined signal
processing on the picture signal and outputs the processed picture signal
to the system controller 102. On the basis of the processed picture
signal, the system controller 102 outputs a display signal for displaying
a picture on the display 103. The display 103 displays a picture based on
the display signal as a captured picture of the object 104 on a screen.

EXAMPLES

First Example

[0063] A high-pressure synthetic diamond produced by Sumitomo Electric
Industries, Ltd. was prepared as a supporting substrate 80 as shown in
FIG. 7A. The supporting substrate 80 had a disc-shape (cylindrical shape)
with a diameter of 5 mm and a thickness of 1 mm. A UV-ozone asher
treatment was performed in advance on the supporting substrate 80 to
remove organic matter present on the surface thereof.

[0064] Then, as shown in FIG. 7B, an interlayer 81 composed of titanium
and niobium was formed on one surface of the two circular surfaces of the
supporting substrate 80 with a diameter of 1 mm by a sputtering method so
as to have a thickness of 100 nm. The deposition of the interlayer 81 by
the sputtering method was performed using sputtering targets composed of
titanium and niobium and Ar as a carrier gas. During the deposition, the
supporting substrate 80 was placed on a stage inside a deposition device
(not shown) and subjected to substrate heating up to 260° C. by a
heater built in the stage. The deposition rate of the interlayer 81 was
controlled so that the amount of niobium added to the supporting
substrate 80 per unit time was 0.821 (in terms of atomic ratio) relative
to the amount of titanium added to the supporting substrate 80 per unit
time. The control of the deposition rate was performed by controlling the
input power to each sputtering target.

[0065] Then, as shown in FIG. 7c, a target layer 82 composed of tungsten
was formed on the interlayer 81 by sputtering so as to have a thickness
of 7 μm. The deposition of the target layer 82 by the sputtering
method was performed continuously without ventilation of the atmosphere
in the deposition device using Ar as a carrier gas. During the deposition
of the target layer 82, the substrate 80 was subjected to substrate
heating up to 260° C. as in the deposition of the interlayer 81.

[0066] Next, the layered body including the supporting substrate 80, the
interlayer 81, and the target layer 82 being stacked on top of one
another in this order was put into an image furnace (not shown) evacuated
to a degree of vacuum of 1E-5 Pa. The layered body was then maintained
within the image furnace at 700° C. for 1 hour. After the heating
step, the image furnace was cooled down to room temperature over 2 hours
and ventilated. Then, the layered body was taken out. Between the step of
forming the target layer 82 and the step of performing β-phase
stabilization treatment, the layered body was put into the image furnace
without introduction of air.

[0067] As described above, a target 8 that included the supporting
substrate 80, the interlayer 81, and the target layer 82 being stacked on
top of one another in this order was manufactured.

[0068] The interlayer 81 and the target layer 82 were formed in a
multilayer so as to respectively have predetermined thicknesses by
controlling the deposition time in accordance with predetermined
calibration curve data based on the relationship between thickness and
deposition time when each layer was formed as a single layer. The
measurement of thickness for determining the calibration curve data was
made using spectroscopic ellipsometer UVISEL ER produced by HORIBA, Ltd.

[0069] The resulting target 8 was die-cut to form intermediate samples
(not shown). The intermediate samples were subjected to mechanical
polishing and FIB processing to be processed into a size so that the
target layer 82, the interlayer 81, and the interface between the
interlayer and the supporting substrate 80 were included therein. Thus, a
cross-section specimen S1 was prepared. As in the case of preparing the
cross-section specimen S1, the intermediate samples were processed using
FIB processing and a SIMS detector in combination to be processed so that
the interlayer 81 stacked on the supporting substrate 80 was exposed.
Thus, a film-surface specimen S2 was prepared.

[0070] The distribution of the composition and bonding of each layer in
the cross-section specimen S1 was visualized on a map using a
transmission electron microscope (TEM) and electron beam spectrometry
(energy dispersive X-ray spectrometry: EDX) in combination. It was
thereby confirmed that a carbon-predominant region corresponding to the
supporting substrate 80, titanium-predominant region corresponding to the
interlayer 81, and tungsten-predominant region corresponding to the
target layer 82 were stacked. The distribution of the composition of the
interlayer 81 in the film-surface specimen S2 was visualized on a map
using the transmission electron microscope (TEM) and electron beam
spectrometry (energy dispersive X-ray spectrometry: EDX) in combination.
It was thereby confirmed that titanium and niobium were distributed in
the same region as each other in both interlayers 81 of the cross-section
specimen S1 and the film-surface specimen S2.

[0071] The thickness of the interlayer 81 in the cross-section specimen S1
was measured using the transmission electron microscope (TEM) and found
to be 100 nm.

[0072] Then, crystallinity, grain size, and composition distribution of
the cross-section specimen S1 and the film-surface specimen S2 were
evaluated by bright-field observation and dark-field observation using
the transmission electron microscope, and by electron beam spectrometry
(energy dispersive X-ray spectrometry: EDX) in combination. As a result,
a plurality of grains were observed in the interlayer 81. The average
grain size thereof was 85 nm. It was confirmed that each grain contained
titanium and niobium. The titanium and niobium contents of the interlayer
81 were 54.9 atm % and 45.1 atm %, respectively.

[0073] The crystal form of the grains in the cross-section specimen S1 and
the film-surface specimen S2 was evaluated by bright-field observation
and dark-field observation using the transmission electron microscope, by
electron diffraction (ED), and by electron beam spectrometry (energy
dispersive X-ray spectrometry: EDX) in combination. The samples were
maintained at 400° C. during evaluation. From the result of the
electron diffraction, it was confirmed that a body-centered cubic crystal
structure predominated in titanium contained in the interlayer 81. In
other words, it was confirmed that the interlayer 81 of this Example
showed the β-phase at 400° C. It was also confirmed that,
even when the samples were kept at a room temperature of 25° C.,
the interlayer 81 showed the β-phase similarly to the result under
the heating condition of 400° C.

[0074] Then, as shown in FIGS. 7D and 7E, the target 8 was fixed with
silver solder (not shown) inside the cylinder of a cylindrical shield 7
composed of tungsten. Note that FIG. 7E is a cross-sectional view
illustrating a unit including the target 8 and the shield 7 shown in a
longitudinal cross-sectional view in FIG. 7D taken along the imaginary
plane VIIE-VIIE.

[0075] Next, as shown in FIGS. 4A and 4B, the unit including the target 8
and the shield 7, and the electron emission source 3 including the
electron emission portion 2 were connected to the envelope 6 so that the
target layer 82 (not shown) and the electron emission portion 2 faced
each other. The envelope 6 was formed by joining a cathode 19 composed of
copper, an anode 20 composed of copper, and an insulating tube 21 that
had a cylindrical shape and composed of ceramics with one another with
silver solder (not shown). The electron emission source 3 was connected
to the cathode 19 through a current introduction terminal 4 prior to
formation of the envelope 6. The target 8 was connected to the anode 20
through the shield 7 prior to formation of the envelope 6. An impregnated
thermionic-emission gun was used as the electron emission source 3. The
envelope 6 was evacuated to a degree of vacuum of 1E-5 Pa with an exhaust
pipe and an evacuator (not shown) and the exhaust pipe was then sealed.
Thus, the radiation generating tube 1 was manufactured. Note that FIG. 4B
is a cross-sectional view illustrating the radiation generating tube 1
shown in a longitudinal cross-sectional view in FIG. 4A taken along
imaginary plane IVB-IVB.

[0076] As shown in FIG. 2, the radiation generating tube 1 was housed in a
package 11 composed of brass together with a driving circuit 14. The
driving circuit 14 and the radiation generating tube 1 were electrically
connected to each other. The package 11 was filled with silicone oil
having a relative dielectric constant of 2.8 (at room temperature, 1 MHz)
and sealed with a brazen lid. Thus, the radiation generating apparatus 13
was manufactured. In addition, the radiation generating apparatus 13 of
this Example included a diamond substrate with a thickness of 300 μm
that was disposed in the opening facing the supporting substrate 80 of
the shield 7 and serves as a radiation extraction window 10.

[0077] As shown in FIG. 2, a measuring system for determining the
intensity of radiation emitted from the manufactured radiation generating
apparatus 13 was constructed as below. Dielectric probes were coupled
with respective connecting lines between the driving circuit 14 and the
radiation generating tube 1. The dielectric probes were connected to a
discharge counter 25 installed outside the package 11. A dosimeter 26 was
disposed on the extension connecting the centers of the electron emission
portion 2 and the target 8 at a distance of 100 cm from the surface of
the supporting substrate 80 in contact with the air toward the air side.
The dosimeter 26 included an ionization chamber and was disposed in order
to measure the time-integrated doses. The discharge counter 25, the
driving circuit 14, and the package 11 were maintained at ground
potential through grounding terminals 16.

[0078] The driving conditions during the stability evaluation of the
radiation generating apparatus 13 were as follows: an accelerating
voltage applied to the target 8 relative to the electron emission portion
2 of +90 kV, a current density of electrons on the irradiated target
layer 82 of 4 mA/mm2, and a pulse driving intermittent electron
irradiation at 10 second intervals. During the stability evaluation of
the output radiation intensity, a current from the target layer 82 to the
grounding electrode was detected and the current density of electrons on
the irradiated target layer was controlled to have a variation
coefficient of 1% or less using a negative feedback circuit (not shown).
During the running evaluation of the radiation generating apparatus 13,
stable running without discharge was confirmed using a running discharge
counter 25.

[0079] The stability evaluation of the output radiation intensity of the
radiation generating apparatus 13 was performed as follows: The electron
emission source 3 was subjected to the pulse driving under the above
conditions. At every 100 hours, the radiation generating apparatus was
temporarily stopped for 2 hours till the entirety of the radiation
generating tube 1 reached a temperature equal to room temperature and the
output radiation intensity was determined with a radiation dosimeter 26.
The output radiation intensity was an average intensity of the signal
detected by the radiation dosimeter 26 over 1 second. The stability
evaluation was conducted using the coefficient of variation obtained by
normalizing the output radiation intensity observed in each time step
with the initial output radiation intensity. These evaluation results are
shown in Table 1.

[0080] It was confirmed that the radiation generating apparatus 13
including the target 8 of this Example provides stable output radiation
intensity even in cases where there is a long driving history.

Second Example

[0081] In this Example, a target 8 was manufactured as in the first
example, except that the deposition rate was controlled in the step of
forming the interlayer 81 so that the amount of niobium added on the
supporting substrate 80 per unit time was 0.176 (in terms of atomic
ratio) relative to the amount of titanium added to the supporting
substrate 80 per unit time.

[0082] Intermediate samples, a cross-section specimen S1, and a
film-surface specimen S2 were prepared as in Example 1 using the target 8
manufactured in this Example.

[0083] As in the first example, mapping of the distribution of composition
and bonding was carried out for each layer of the prepared cross-section
specimen S1 using the TEM and EDX in combination. It was thereby
confirmed that a carbon-predominant region corresponding to the
supporting substrate 80, titanium-predominant region corresponding to the
interlayer 81, and tungsten-predominant region corresponding to the
target layer 82 were stacked. Next, as in the first example, mapping of
the composition distribution of the interlayer 81 in the film-surface
specimen S2 was carried out using the TEM and EDX in combination. It was
thereby confirmed that titanium and niobium were distributed in the same
region as each other in both interlayers 81 of the cross-section specimen
S1 and the film-surface specimen S2.

[0084] As in the first example, the thickness of the interlayer 81 in the
cross-section specimen S1 was measured using the TEM and found to be 99
nm.

[0085] As in the first example, crystallinity, grain size, and composition
distribution of the cross-section specimen S1 and the film-surface
specimen S2 were evaluated by bright-field observation and dark-field
observation using the TEM, and by EDX in combination. As a result, a
plurality of grains were observed in the interlayer 81. The average grain
size thereof was 103 nm. It was confirmed that each grain contained
titanium and niobium. The titanium and niobium contents of the interlayer
81 were 85.0 atm % and 15.0 atm %, respectively.

[0086] As in the first example, the crystal form of the grains in the
cross-section specimen S1 and the film-surface specimen S2 was evaluated
by bright-field observation and dark-field observation using the TEM, by
ED, and by EDX in combination. The samples were maintained at 400°
C. during evaluation. From the result of the electron diffraction, it was
confirmed that the titanium contained in the interlayer 81 had a crystal
form including both the grains with a body-centered cubic structure and
the grains with a hexagonal close-packed structure. In other words, it
was confirmed that the interlayer 81 in this Example was in the
α-β eutectoid phase at 400° C. and showed the
β-phase. It was also confirmed that, even when the samples were kept
at a room temperature of 25° C., the interlayer 81 was in the
α-β eutectoid phase and showed the β-phase similarly to
the result under the heating condition of 400° C.

[0087] As in the first example, as shown in FIGS. 4A and 4B, a radiation
generating tube 1 including the target 8 was manufactured. Then, as shown
in FIG. 2, a radiation generating apparatus 13 including the radiation
generating tube 1 was then manufactured.

[0088] As in the first example, the stability evaluation of the output
radiation intensity was also conducted in this Example using the
experimental system shown in FIG. 2. The results are shown in Table 2.

[0089] It was confirmed that the radiation generating apparatus 13
including the target 8 of this Example provides stable output radiation
intensity even in cases where there is a long driving history.

Third Example

[0090] In this Example, a target 8 was manufactured as in the first
example, except that the sputtering target composed of vanadium was used
in place of that composed of niobium and that the deposition rate was
controlled in the step of forming the interlayer 81 so that the amount of
vanadium added on the supporting substrate 80 per unit time was 0.25 (in
terms of atomic ratio) relative to the amount of titanium added on the
supporting substrate 80 per unit time.

[0091] Intermediate samples, a cross-section specimen S1, and a
film-surface specimen S2 were prepared as in Example 1 using the target 8
manufactured in this Example.

[0092] As in the first example, mapping of the distribution of composition
and bonding was carried out for each layer of the prepared cross-section
specimen S1 using the TEM and EDX in combination. It was thereby
confirmed that a carbon-predominant region corresponding to the
supporting substrate 80, titanium-predominant region corresponding to the
interlayer 81, and tungsten-predominant region corresponding to the
target layer 82 were stacked. Next, as in the first example, mapping of
the composition distribution of the interlayer 81 in the film-surface
specimen S2 was carried out using the TEM and EDX in combination. It was
thereby confirmed that titanium and vanadium were distributed in the same
region as each other in both the interlayers 81 of the cross-section
specimen S1 and the film-surface specimen S2.

[0093] As in the first example, the thickness of the interlayer 81 in the
cross-section specimen S1 was measured using the TEM and found to be 100
nm.

[0094] As in the first example, crystallinity, grain size, and composition
distribution of the cross-section specimen S1 and the film-surface
specimen S2 were evaluated by bright-field observation and dark-field
observation using the TEM, and by EDX in combination. As a result, a
plurality of grains were observed in the interlayer 81. The average grain
size thereof was 91 nm. It was confirmed that each grain contained
titanium and vanadium. The titanium and vanadium contents of the
interlayer 81 were 80.2 atm % and 19.8 atm %, respectively.

[0095] As in the first example, the crystal form of the grains in the
cross-section specimen S1 and the film-surface specimen S2 was evaluated
by bright-field observation and dark-field observation using the TEM, by
ED, and by EDX in combination. The samples were maintained at 400°
C. during evaluation. From the result of the electron diffraction, it was
confirmed that the titanium contained in the interlayer 81 had a crystal
form including both the grains with a body-centered cubic structure and
the grains with a hexagonal close-packed structure. In other words, it
was confirmed that the interlayer 81 in this Example was in the
α-β eutectoid phase at 400° C. and showed the
β-phase. It was also confirmed that, even when the samples were kept
at a room temperature of 25° C., the interlayer 81 was in the
α-β eutectoid phase and showed the β-phase similarly to
the result under the heating condition of 400° C.

[0096] As in the first example, as shown in FIGS. 4A and 4B, a radiation
generating tube 1 including the target 8 was manufactured. Then, as shown
in FIG. 2, a radiation generating apparatus 13 including the radiation
generating tube 1 was then manufactured.

[0097] As in the first example, the stability evaluation of the output
radiation intensity was also conducted in this Example using the
experimental system shown in FIG. 2. The results are shown in Table 3.

[0098] It was confirmed that the radiation generating apparatus 13
including the target 8 of this Example provides stable output radiation
intensity even in cases where there is a long driving history.

Fourth Example

[0099] This Example employed the same method as in the first example,
except that the stability evaluation of the output radiation intensity
from the radiation generating tube 1 was conducted using the radiation
generating tube 1 manufactured in the first example and the measuring
system illustrated in FIG. 5. The results are shown in Table 4.

[0100] It was confirmed that the radiation generating tube 1 including the
target 8 of this Example provides stable output radiation intensity even
in cases where there is a long driving history.

Comparative Example

[0101] In this Comparative example, a target 48 was manufactured as in the
first example, except that the deposition rate was controlled in the step
of forming the interlayer 81 so that the amount of niobium added to the
supporting substrate 80 per unit time was 0.010 (in terms of atomic
ratio) relative to the amount of titanium added to the supporting
substrate 80 per unit time.

[0102] The intermediate samples, the cross-section specimen S1, and the
film-surface specimen S2 were prepared as in the first example using the
target 48 manufactured in this Comparative example.

[0103] As in the first example, mapping of the distribution of composition
and bonding was carried out for each layer of the prepared cross-section
specimen S1 using the TEM and EDX in combination. It was thereby
confirmed that a carbon-predominant region corresponding to the
supporting substrate 80, titanium-predominant region corresponding to the
interlayer 81, and tungsten-predominant region corresponding to the
target layer 82 were stacked. Next, as in the first example, mapping of
the composition distribution of the interlayer 81 in the film-surface
specimen S2 was carried out using the TEM and EDX in combination. It was
thereby confirmed that titanium and niobium are distributed in the same
region as each other in both the interlayers 81 of the cross-section
specimen S1 and the film-surface specimen S2.

[0104] As in the first example, the thickness of the interlayer 81 in the
cross-section specimen S1 was measured using the TEM and found to be 99
nm.

[0105] As in the first example, crystallinity, grain size, and composition
distribution of the cross-section specimen S1 and the film-surface
specimen S2 were evaluated by bright-field observation and dark-field
observation using the TEM, and by EDX in combination. As a result, a
plurality of grains were observed in the interlayer 81. The average grain
size thereof was 139 nm. It was confirmed that each grain contained
titanium and niobium. The titanium and niobium contents of the interlayer
81 were 99.0 atm % and 1.0 atm %, respectively.

[0106] As in the first example, the crystal form of the grains in the
cross-section specimen S1 and the film-surface specimen S2 was evaluated
by bright-field observation and dark-field observation using the TEM, by
ED, and by EDX in combination. The samples were maintained at 400°
C. during evaluation. From the result of the electron diffraction, it was
confirmed that the titanium contained in the interlayer 81 had a crystal
form including only grains with a hexagonal close-packed structure. In
other words, it was confirmed that the interlayer 81 in this Comparative
example shows the α-phase at 400° C. but not the
β-phase. It was also confirmed that, even when the samples were kept
at a room temperature of 25° C., the interlayer 81 showed the
a-phase but not the β-phase similarly to the result under the
heating condition of 400° C. As in the first example, as shown in
FIGS. 4A and 4B, the radiation generating tube 41 including the target 8
was manufactured. Then, as shown in FIG. 2, the radiation generating
apparatus 43 including the radiation generating tube 41 was then
manufactured.

[0107] As in the first example, the stability evaluation of the output
radiation intensity was also conducted in this Comparative example using
the experimental system shown in FIG. 2. The results are shown in Table
5.

[0108] It was confirmed that the radiation generating apparatus 13
including the target 8 of this Comparative example provides less stable
output radiation intensity compared with that of Examples 1 to 4 in cases
where there is a long driving history.

[0109] According to the present invention, it is possible to maintain
stable adhesion between the supporting substrate and the target layer
even over a prolonged period of operation, which results in a reduction
in the variation in the output radiation intensity caused by temperature
rise of the target layer. Thus, it is possible to provide a radiation
target having highly-reliable radiation emission characteristics.

[0110] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0111] This application claims the benefit of International Patent
Application No. PCT/JP2012/051297, filed Jan. 23, 2012, which is hereby
incorporated by reference herein in its entirety.